Oscillation generator with automatic frequency control



OSCILLATION GENERATOR WITH AUTOMATIC FREQUENCY CONTROL Filed May 21, 1923 2. Sheets-Sheet 1 D1 g, H E, #7

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Jaseph W HOf/O/j by Af/j/ Feb. 8, 1927.

1,616,622 J. w. HORTON OSCILLATION GENERATOR WITH AUTOMATIC FREQUENCY CONTROL Filed May 21. 1923 2 Sheets-Sheet 2 22 39 fig 5 24 34 ,}-lwb fli m5 arc.

Joseph WHOf/Of) by AW mama Feb. 8, v192-1.

UNITED STATES PATENT OFFICE.

oann w. non'ron, or BLoomrmLn, NEW JERSEY, Assmnon 'ro wns'rmm ELECTRIC COMPANY, mconronurnn, on NEW YORK, n. Y., A CORPORATION or NEW YORK.

OSCILLATION GENERATOR WITH AUTOMATIC FREQUENCY CONTROL Application filed May 21, 1923i Serial No. 640,363.

This invention relates to oscillation generators, and more particularly, to means associated with such generators whereby oscillations of substantially unvarying frequency are produced. a

The development of oscillation generators has now reached the point where it is possible to obtain a circuit in which the frequency is determined almost entirely by the resonant element. In fact the frequency is controlled to such an extent by the inductance and capacity of the resonant circuit that the most serious frequency variations are caused by changes of these quantities with temperature.

An object of this invention is the provision of means associated with the resonant element of an electron tube generator for automatically compensating for effects of temperature change.

A feature relates to a variable condenser controlled by a thermal element whereby a substantially parabolic relation between change of'capacity with change of temperature is obtained. In other words, the capacity varies substant ally as the square of the temperature.

A further object has reference to carrier current signaling systems utilizing separate oscillators at transmitting and receiving terminals and to improvements in these oscillators whereby the frequencies generated at opposite terminals of the same channel are held at substantially the same value under varying conditions.

The generator of this invention is characterized by a resonant circuit having a variable condenser controlled by a thermal element sensitive to change of temperature. This condenser may be of any desired type but it ispreferred for purposes of this invention to use an air condenser constructed of three sets of semi-circular metallic plates. One set of plates may be fixed; another set may be movable transversely under the action of a thermal device; and a third set may be rotatable between the first two sets. The fixed and transversely movable sets may comprise groups of plates of semi-circular shape with corresponding plates of each group normally positioned with their straight edges adjacent to each other and their surfaces in the same plane. The third group may consist of semi-circular plates interspaced between the first two sets and mounted upon a rotatable supporting member co-axial with the center of all the semicircular plates.

As the temperature changes the thermal element contracts or expands thereby transversely moving the plates of its associated group. This movement changes the spacmg of this group with respect to the other plates and thus produces a corresponding change of capacity. The action of the condenser when associated with an oscillation generator and properly adjusted will serve to compensatefor simultaneous change in the reactance of other portions of its resonant circuit.

For a clearer understanding of the nature of this invention and the additional features and objects thereof, reference should be made to the following detailed description taken in connection with the accompanying drawings, of which Fig. 1 is a diagram illustrating the principle upon which the variable condenser operates; Fig. 2 is a plan view of a practical form of the variable condenser; Fig. 3 is a front View partly in section of the same; Fig. 4 is a graph which illustrates the relation of capacity to temperature of the condenser of Figs. 2 and 3; Fig. 5 is a graph illustrating the relation between frequency and temperature in an oscillation circuit; Fig. 6 shows a combined oscillatormodulator embodying this invention; Fig. 7 is a circuit showing the application of this invention to the uses of carrier current telephony.

The arrangement shown in Fig. l is a condenser comprising three metallic plates, A, B and C, plates A and C being connected together. Plates A and B are movable in the directions indicated b the arrows. When plates A and C are in lme, it is apparent that motion of plate B in the directions indicated by the arrow will cause no change of capacity between itself and plates A and G. However, should plate A be moved out of alignment with plate C in either direction indicated by the arrow, thenany subsequent movement of plate B will produce a change of capacity. The percentage change of capacity for a given motion of plate A will depend upon the position of plate B.

In Figs. 2 and 3 are shown two views of an air condenser constructed to operate upon the principle illustrated in Fig. 1. Groups of plates A,, B, and C, corresponding to plates A, B and C of Fig. 1 are mounted upon the base 1 of Fig. 3. Plates 0, are held spaced in the usual manner by a metallic support 6. Plates A, are mounted in a similar manner upon the transversely movable supporting member 7 also metallic. Plates A, and C, are connectively associated with a common terminal 4. Plates B, are likewise connectively associated with a second terminal 5.

A thermal element 8 is operably associated with member 7 and ma be of any well known type in which motion is produced by the action of temperature variation. Plates B,,which areinterspaced between the groups of plates A, and C are mounted upon a rotatable supporting member 12 provided with. a knob or handle 9 and insulated from me tallic base 1 by a bearing member 13.

Referring to Fig. 4, D. F. G. is a. curve which shows graphically the general relation between the change of capacity caused by movement of plates A, under the action of thermal element 8 and the change of temperature producing the motion for a given adjustment of plates 13,. An equation of the form I expresses mathematically the same relation.

In this equation C is capacity, K is a constant depending upon the physical characteristics of the particular condenser, S is the distance between the plates A, of Fig. 3, X is the distance between the plates B, and the nearest adjacent plate A, in Fig. 3, and is a function of the temperature of the condenser including the thermal element 8. This curve and equation are applicable to a condenser of the type shown in Fig. 3 where the capacity varies substantially as the square of the temperature.

From the curve, it is apparent that up to a given temperature, the capacity decreases as the temperature increases, but beyond a critical point T the capacity increases with increase of temperature.

In the oscillator of this invention, it is preferred to operate only at temperatures within a range corresponding to T,,-O of Fig. 4. The degree of temperature at which the critical point T occurs depends upon the construction of the condenser and the thermal element. 1

Fig. 5 shows the eneral form of a. curve illustrating the relationship between change of frequency with change of temperature of a resonant circuit.

Let us assume for example, that the variable condenser of Fig. 3 is included in a resonant circuit and is so constructed that at temperature '1, thermal element 8 holds plates A, in line with plates C, and that in this po- Fig. 5, a resulting change in its impedance producing a corresponding change of frequency. represented by the line D, IE, will ordinarily take place. This change of fre quency may be caused by change in the electrical constants of any element or combination of elements forming a portion of the oscillatory system. If, on the other hand, the variable condenser of Fig. 3 having characteristics as indicated by the curve of Fig. 4 forms a part of the resonant circuit, then at this change of temperature the thermal element 8 will move plates A, out of alignment with plates C, by an amount which causes a change of capacit represented by the line D--E of Fig. 4. his change of capacity tends to hold the frequency at its original value. This value may be exactly obtained by adjustment of plates B, which now results in a change of capacity, since plates A, and O, are no longer in alignment.

From the curve of Fig. 4 another curve showing the relation between the capacity of the thermally controlled condenser and the temperature, another curve may be obtained showing the relation between the frequency of the oscillatory system as determined by this condenser alone and the temperature. lhis curve is shown by the dotted line of Fig. 5. The full curve D. F. of Fig. 5 shows the relation between the frequency of the oscillation system, as determined by elements other than the thermally controlled condenser, and temperature. At the temperature T, it is evident that the reduction in frequency caused by this thermally controlled condenser is numerically equal to the increase in frequency caused by changes in other circuit elements. However, the nearer the dot-ted curve of Fig. 5 approaches symmetry with the full curve D, F,, the more closely will the frequency of the oscillator be maintained at its original value. Obviously, for temperatures above T the compensation produced by the variable condenser is no longer in the right direction.

Fig. 6 shows the application of this invention to a combined modulator oscillator. In this figure 22 and 23 are three electrode vacuum tubes having symmetrical input circuits 24 and 25 connected res ectively to their grid electrodes. This modulator also comprises out ut circuits 34 and 35 associated with the p ate electrodes of tubes 22 and 23 from line 27 to the input circuits. In addition these circuits comprise a common lead connected to the filaments of tubes 22 and 23 having a polarizing source 28 and one winding of the transformer 29 therein. The other winding of transformer 29 forms a portion of a resonant circuit 30 containing an adjustable condenser 31 and a variable condenser 32 of the type shown and dcscribed in connection with Fig. 3. The resonant circuit 30 is connectively associated with output circuits 34 and 35 by a feedback circuit 33, having a resistance included therein for controlling the amount of feedback energy.

Output circuits 34 and 35 comprise in addition to the plate circuit battery 36 and impedance coils 37 and 38, a transformer 39. The secondary of this transformer is connected to a line 40 to which modulated higl'i frequency oscillations may be supplied.

In consequence of energv from output oncuits 34 and 35 supplied to resonant circuit 30 by way of feedback circuit 33, sustained oscillations are generated therein. These oscillations are supplied to input circuits 24 and 25 through transformer 29 and may be modulated in accordance with low frequency waves incoming over line 27 in a well known manner. The resulting modulated current is supplied from output circuits 34 and 35 to tranformer 39 and through it to line 40.

In Fig. 7'is shown the terminal circuit of a two-way channel in a carrier current telephone system. A low frequency line LFL is associated with a transmitting channel TC and a receiving channel BC by means of a balanced transformer or hybrid coil 11. In order that channels TC and RC may be con jugate with respect to each other, that is in order that electrical changes in one channel may not produce effects in the other channel, an artificial line or network N is rovided that is equivalent electrically to llne LFL and its associated equipment.

In 'order that low frequency currents incoming over line LFL may be translated into modulated high frequency carrier currents a modulator M is provided in transmitting channel TC. This modulator may be of the general type shown in the patent to John R. Carson No. 1,343,307, dated June 15, 1920. In accordance with the description given in this patent, this modulator is of the balanced type in which the unmodulated carrier oscillations are normally suppressed. However, when low frequency currents transmitted over line LFL are impressed upon modulator M, carrier oscillations are transmitted having an amplitude proportional to that of the low frequency wave.

For supplying carrier oscillations, modulator M is provided with an oscillator) comprising a three-electrode tube 10 having an input circuit 15, associated with its grid electrode and an output circuit 16 for supplying carrier oscillations to be modulated, connectively associated with its plate electrode. A feed back circuit 3 comprising a resonant circuit 2 joins the input and output circuits, whereby energy is supplied from the output circuit to the input. circuit for maintaining sustained oscillations. Resonant circuit 2 is provided with a condenser 14 preferably of the type shown and dcscribcd in connection with Fig. 3.

In addition to the modulator M and associated oscillator O, transmitting channel TC comprises a transmitting band filter TBF of the general type described in patent to George A. Campbell No. 1,227,113, dated May 22, 1917. This band filter is designed to transmit a band of frequencies ranging above or below the carrier frequency of the channel by an amount equal to the range of frequencies normally utilized in ordinary telephonic transmission. Modulated carrier currents produced in transmitting channel TC are transmitted to high frequency line ML over common transmitting channel CTC. This common transmitting channel'serves also as a means for transmitting modulated carrier currents to high frequency line ML from other transmitting channels similar to TC, which may be connected at points TC and TC.

The common transmitting channel is provided with a transmitting terminal amplifier TTA which is preferably of the thermionic type. This amplifier may be arranged in two stages, resistance coupled with the wellknown push-pull connection as illustrated in Fig. 22 of the paper on carrier current Telephony and Telegraphy by E. H. Colpitts and O. B. Blackwell published in the T ransactions of the American Institute of Electrical Engineers, volume 40, p. 411, 1921.

In addition, common transmitting channel CTC comprises a group filter GF This group filter may be of the general type shown in patent to George A. Campbell No. 1,227,113 dated May 22, 1917, and designed to transmit a group of frequencies including the range within which lie all the transmitting channel frequencies and to substantially exclude all others.

For translating incoming modulated carrier oscillations into low frequency telephonic currents, receiving channel RC 18 provided with a demodulator DM and an associated oscillator 0, similar to oscillator 0 described above. The demodulator DM is preferably of the duplex vacuum tube type disclosed in patent to John R. Carson No. 1.343308, dated June 15, 1920. This demodulator operates by the so-called homodyne method in which it is required that scillations of the frequency of the carrier oscillations supplied to the corresponding modulator be likewise supplied to the demodulator. Associated with demodulator Div-f is an oscillator (i similar to oscillator 0 and adapted to produce oscillations of the same frequency as oscillator O. The resonant element of the oscillator also contains a variable condenser of the type shown in Fig. 3.

Receiving channel Rt) comprises in addi tion to demodulator DM :1 receiving band filter RBF which may be of the same general type as the transmitting band filter TBF.

Modulated high frequency oscillations incoming from line ML are transmitted to receiving channel RC through common receiving channel CRC. These h gh frequency modulated oscillations are prevented from entering common transmitting channel OTC by the action of group filter GF Common receiving channel ORG comprises a group filter Gil which may be of the same general types as GF but designed to exclude the group of frequencies utilized in the transmitting channels TC, TC etc., and to transmit the group of frequencies utilized by receiving channels RC, RC etc. In addition to the group filter GF common receiving channel ORG comprises receiving terminal amplifier RTA which may be of the same general type as the transmitting terminal amplifier TTA which is designed to eliiciently amplify modulated high frequency oscillations.

In the operation of this system, carrier frequencies above a certain value and separated by an amount somewhat greater than the range of frequencies utilized for ordinary telephonic transmission are assigned to transmitting channels. In a like manner, frequencies below this arbitrary value and separated by similar ranges are utilized in the receiving channels. It will be evident that with the homodyne method of demodulation utilized in this system, the frequency of the carrier supplied by oscillator O to the modulator M of transmitting channel TC must at all times be equal to the frequency of the oscillator supplying the demodulator of the corresponding receiving channel. This synchronism between the frequencies of the oscillations independently generated at opposite ends of the same channel is maintained by the action of the variable eondenser of this invention placed in the resonant circuits of the respective oscillators.

Since effects of temperature change upon the resonant circuits of the oscillators are responsible for the greatest frequency variation, it will be seen that the action of the variable condenser of this invention in compensating for effects of temperature change upon the resonance circuits as already explained may be such as to maintain a. high degree of synchronism between oscillators even when situated at widely separated points and under differently varying conditions of temperature.

Although this invention has been described and illustrated in relation to specific circuit arrangements, it will'be evident that it is capable of application in numerous other organizations of widely different character. The invention is therefore not to be limited to the particular embodiments disclosed, but only by the appended claims.

What is claimed is:

1. A generator comprising a space discharge device, a resonant element and an adjustable reactance element associated therewith, and means responsive to temperature change for controlling the adjustment, of said reactant-e, whereb waves of constant frequency are generate 2. A generator comprising a space discharge device, a tuned circuit including an adjustable condenser, and means, responsive to temperature change, for varying the adj ustment of said condenser,'whereby energy of constant frequency is obtained.

3. The combination with a generator, ineluding a space discharge device, of a resonant element and a spaced plate condenser, and means, responsive to temperature changes, for varying the spacing of the plates to provide a capacity, adapted to maintain substantially constant the frequency of oscillations generated.

4. The combination with an oscillation generator of the electron tube type of a resonant circuit, a variable reactance elementsensitive to temperature variation associated therewith, and means for adjusting the sensitivity of said reactance element to change of temperature.

5. The method of operating a generator, including a space discharge device and a spaced plate condenser, which com rises automatically varying the spacing o the condenser plates, responsive .to temperature change, for securing substantially constant frequency waves.

6. The method of control of the frequency of the oscillations of a generator circuit including a s ace discharge and a resonant element inc uding an adjustable reactance device, which comprises adjusting the sensitivity of said device to a desired 1 value, and, responsive to change of temperature, automatically adjustin said reactanoe to compensate for opposite e anges in the reactance of other portions of said generator circuit.

1. 1mi u 7. The method of producing changes with temperature in substantially oscillations of substantially constant per1- direct proportion to corresponding change odic time, in a. space discharge tube generin the reactance of other portions of said 10 ator including a tuned circuit, which comtuned-circuit.

I prises introducing, into the tuned circuit, In witness whereof, I hereunto subscribe a condenser the capacity of which supplemy 'name this 14th da of MayA. D., 1923. ments the capacity of the tuned circuit and JOS PH W. HORTON. 

